The present invention relates to a magnetic tape cassette and, more particularly, to a magnetic tape cassette having a separate guide block which is inserted between top and bottom cover plates for guiding a tape along an open front of the tape cassette.
A conventional magnetic tape cassette is usually formed by a two-piece plastic case that is assembled by joining top and bottom half cases of substantially the same configurations, which are made of plastic material by molding. However, such plastic half cases having rather complicated configurations tend to warp due to thermal deformations and molding strains of the plastic material. Accordingly, an assembled case often involves problems such as an irregular tape run and an off-track or out-of-phase recording or play, in the tape cassette.
In order to remove these problems, to prevent the warp of the cassette case, to improve acoustic performances of the tape cassette and to increase mechanical strength of the case, a three-piece cassette case has been proposed in U.S. Pat. Nos. 4,267,986 (Uemura et al.) and 4,330,068 (Shoji), assigned to the same assignee as this application.
However, in the proposed cassette cases comprising top and bottom cover plates and an intermediate frame inserted therebetween, the intermediate frame having a thin rectangular ring form is provided with a plurality of projections on its front for guiding a tape. Hence, the intermediate frame functions not only as a frame but also as a tape guide. By functioning as the frame, the increases of the mechanical strength and the weight of the case and the prevention of the deformation of the case may be attained. It has been proven that the increase of weight prevents the cause of unnecessary resonance or vibration, with the result of a better acoustic performance. By functioning as the tape guide, a proper friction is imparted between the running tape and the contact surface of the tape guide part, which is essential for properly determining its shape and increasing its accuracy.
Thus, in the prior art, the intermediate frame has been required to function as a frame as well as a tape guide, but the functions of these two members sometimes contradict each other. In other words, in this case, the functions as the frame and as the tape guide can be attained together to only a limited degree or only by sacrificing one or the other at the same time.
In U.S. Pat. No. 4,506,846 (Gelardi et al.), a tape cassette comprising top and bottom plastic half cases and a separate tape guide for guiding a tape along the open front of the tape cassette is disclosed. In this case, the tape guide is made in a simple form to attain an accurate structure. However, since the cassette case is mainly composed of the top and bottom plastic half cases, even when the functioning of the tape guide is excellent, there are problems in the functioning of the frame. For instance, the insufficient mechanical strength of the case may cause it to bend. Further, the weight deficiency of the case is liable to cause unnecessary resonance or vibration, a problem in the acoustic performance.